Generally, this invention relates to a device for sensing a predetermined liquid level in a first vessel and for the concomitant actuation of a valve to effect transfer of liquid to the first vessel from a second vessel.
The maintenance of a selected liquid level in a storage vessel is critical when the vessel is used to store materials which will deteriorate when exposed to ambient temperatures. Such materials include: biological substances, e.g. semen, viscera and epidermal tissue; x-ray and gamma-ray detectors, infrared detectors and thermal shielding for a variety of superconducting equipment. Such storage generally entails containering the material an submerging the container in a cryogenic liquid such as liquid nitrogen. Usually, the vessel used is an unpressurized Dewar type vessel which allows for venting of vapor coming from the cyrogenic liquid. As the vaporization continues over time, the liquid level will fall and, if the liquid is not replenished, its level will expose greater and greater portions of the containers. Such exposure will ultimately submit the containered materials to ruinous temperatures. To insure the proper liquid level in the storage vessel, the prior art has provided for monitoring of the storage vessel liquid level and for a reservoir vessel to be connected to the storage vessel by way of a valved transfer line. Monitoring of the liquid level in the storage vessel can be made by visual observation or by the use of mechanical or electrical liquid level sensors in the storage vessel. If the liquid level indicates that replenishment from the reservoir vessel is needed, the transfer line valve is set to the "ON" position and the cryogenic liquid is transferred from the reservoir vessel to the storage vessel by conventional means, such as by providing a head pressure over the liquid in the reservoir vessel, pumping or gravity flow. Setting the valve can be effected manually or can be electrical activated in response to the liquid level sensors. In either case, the reliability of liquid level maintenance is not high especially if the storage period is long, say from 6 months to 10 years. Visual monitoring requires personnel to be on duty at all times which may not always be possible. The use of liquid level sensors and electrically activated valves depends upon a line or battery source for the electricity. Line electricity is notorious for interruptions while battery supplied electricity is dependent upon the integrity and the discharge state of the battery.
Therefore, it is an object of this invention to provide a highly reliable, essentially labor-free, non electrical, liquid level monitoring and valving device for effecting the transfer of liquid to a first vessel from a second vessel so as to maintain a predetermined minimum liquid level in the first vessel.